In recent years, an electric vehicle (EV) and a hybrid vehicle have been widely used. A lithium ion battery and a nickel hydride battery have been widely used as a vehicular secondary battery. The secondary battery needs management of a voltage, a current, and a temperature, and particularly the lithium ion battery demands strict management. When overvoltage or overcurrent is occurred, a burden is imposed on the battery, thereby shortening battery life. Accordingly, when detecting these abnormalities, a battery management device controls such that the secondary battery is electrically disconnected from a vehicle side by opening a contactor, to protect the secondary battery (refer to PTL 1, for example).
To more reliably make control for opening the contactor in detection of overvoltage, a redundant configuration in which two overvoltage detection circuits are provided in parallel is often used.